1. Field of the Invention
The present disclosure relates to a circuit breaker for extinguishing an arc with compressed insulating gas when a fault current occurs in a power system to block the fault current.
2. Description of the Related Art
Gas Insulator Switchgear (GIS) may switch a load current under a normal use condition for a power system.
Furthermore, the gas insulator switchgear is a device capable of safely switching and protecting a line even in an abnormal state such as a fault, a short circuit current, or the like.
The gas insulator switchgear may be configured with a circuit breaker, a disconnecting switch, a grounding switch, an instrument transformer, a lightning arrester, a busbar and the like in a sealed metal tank filled with insulating gas SF6.
Among the internal constituent elements of the gas insulator switchgear, a circuit breaker is a device capable of speedily and safely blocking a fault current to protect a system and various power devices when a failure occurs in the power system.
Here, allowing the circuit breaker to block a fault current denotes extinguishing an arc occurring between two contacts while blocking the fault current.
FIG. 1A is a schematic view illustrating the operation state of a puffer extinction type circuit breaker, and is a connected state between the breaker contacts, and FIG. 1B is a schematic view illustrating the operation state of a puffer extinction type circuit breaker and is a disconnected state between the breaker contacts.
In FIGS. 1A and 1B, the circuit breaker may include a stationary portion 20 and a movable portion 30 disposed to face each other in an axial direction in a tank 1 filled with an insulating gas.
Here, the movable portion 30 may be connected to an actuator 35 to be movable in an axial direction by the actuator 35.
The stationary portion 20 may be fixed to one side within the tank 10.
The stationary portion may include a stationary contactor 21 and a stationary arc contactor.
The stationary contactor 21 may be provided with a stationary main contact 21a and formed with a hollow pipe shape.
The stationary arc contactor 22 may be installed within the stationary contactor 21.
The stationary arc contactor 22 may be provided with a stationary arc contact 22a at a front end portion thereof.
The movable portion 30 may include a puffer cylinder 31, a moving main contact, a moving nozzle, and an operating rod.
The puffer cylinder 31 may have a compression chamber therewithin.
The moving main contact 32 and moving nozzle 33 may be disposed and assembled at an end portion of the puffer cylinder to be brought into contact with each other in an axial direction.
The moving main contact 32 and moving nozzle 33 may be disposed in a concentric manner.
The moving main contact 32 may be disposed outside.
The moving nozzle 33 may be disposed to be inserted into the moving main contact.
The operating rod 34 may include a moving arc contact 34a at a front end thereof.
The operating rod 34 may connect the moving main contact 32 to the actuator 35 such that the stationary arc contact 22a and moving arc contact 34a are brought into contact with or separated from each other.
Here, the moving main contact 32, moving nozzle 33 and puffer cylinder 31 in the movable portion 30 are conductive conductors through which a current flow.
The moving main contact 32 is disposed to be brought into contact with the inside of the stationary main contact 21a to flow a normal current during the contact.
The puffer cylinder 31 may be provided with a piston 36 fixed and provided therein.
The puffer cylinder 31 may be movable by the actuator 35.
When the puffer cylinder 31 is moved in a right direction (based on FIG. 1A) by the actuator 35, it may compress insulating gas within the compression chamber.
Here, the piston 36 may be fixed by a piston rod 37 fixed and provided at the other side within the tank 10.
The moving nozzle 33 may be connected to the compression chamber in a communication manner.
When the stationary arc contact 22a and moving arc contact 34a are separated from each other, the compressed insulating gas is injected through the moving nozzle 33 to extinguish an arc generated between the stationary arc contact 22a and moving arc contact 34a. 
The arc extinction principle of a circuit breaker having the foregoing configuration will be described as follows.
As illustrated in FIG. 1A, the moving main contact 32 and moving arc contact 34a of the movable portion 30 are connected to the stationary main contact 21a and stationary arc contact 22a of the stationary portion 20, respectively, to flow a normal current while maintaining a state that each contact between the movable portion 30 and stationary portion 20 is connected to each other.
However, as illustrated in FIG. 1B, abnormality may occur in a power system.
In this case, when a fault current several times greater than the normal current flows, a driving coil of the actuator 35 is magnetized by the fault current, and the switch of the actuator 35 is operated by an electromagnetic force generated from the coil to move the movable portion 30 in a right direction.
Subsequently, as insulating gas filled in the compression chamber is compressed by the piston 36, and moved in a direction of being away from the stationary portion 20, the stationary arc contact 22a is separated from the moving arc contact 34a. 
Subsequently, an arc is generated between the separated stationary arc contact 22a and moving arc contact 34a, and insulating gas compressed in the compression chamber of the puffer cylinder 31 is ejected between the moving nozzle 33 and moving arc contact 34a, and the arc is extinguished with the ejected insulating gas to block a fault current.
On the other hand, more specifically considering the assembly structure of the movable portion 30 provided within the circuit breaker with reference to FIG. 1A, the moving main contact 32 and moving nozzle 33 are fastened to an end portion of the puffer cylinder 31 by bolts 38a, 38b, respectively.
Here, the moving main contact 32 is brought into contact with an end portion of the puffer cylinder 31 on a first joint surface 31a, and the moving nozzle 33 is brought into contact with an end portion of the puffer cylinder 31 on a second joint surface 31b. 
At this time, the first joint surface 31a and second joint surface 31b are located on the same vertical surface but the first joint surface 31a is located at the outside and the second joint surface 31b at the inside in a radial direction.
The first joint surface 31a and second joint surface 31b of the puffer cylinder 31 are a conductive contactsurface for flowing a current, and thus required to secure a large conductive area to the maximum extent on the first joint surface 31a and second joint surface 31b. 
The area of the joint surface 31a, second joint surface 31b should be increased to secure the largest conductive area of the first joint surface 31a and second joint surface 31b to the maximum extent.
However, in a circuit breaker in the related art, since the diameter of the puffer cylinder 31 is increased as increasing the area of the joint surface 31a, 31b, the volume of the puffer cylinder 31 is increased.
Furthermore, there is a problem in which the fabrication cost of the puffer cylinder 31 and the energy of the actuator 35 for moving the movable portion 30 are increased.
Furthermore, FIG. 2 is an enlarged cross-sectional view illustrating a movable portion in a circuit breaker according to another embodiment of the related art, wherein an end portion (a right end portion based on FIG. 2) of the puffer cylinder 41 and a moving main contact 42 may be combined and brought into contact with each other by a first bolt 44a on the first joint surface 41a. 
A coupling portion may be protruded and formed on an end portion (a left end portion based on FIG. 2) of the moving nozzle 43.
The coupling portion may be inserted and combined with an insertion groove formed between the moving main contact 42 and an end portion of the puffer cylinder 41.
A coupling protrusion to be protruded within the puffer cylinder 41 may be fastened to one surface of the coupling portion by a second bolt 44b. 
In addition, the moving main contact 42 may be coupled to the other surface of the coupling portion on a third joint surface 44c. 
Here, the moving nozzle 43 receives a force in the direction of the coupling portion 43a (in a right direction on the drawing) from the puffer cylinder 41 by the second bolt 44b fastened to the second joint surface 41b, and receives a force in the direction of the coupling portion 43a (in a left direction on the drawing) from the moving main contact 42 by the first bolt 44a fastened to the first joint surface 41a. 
However, three joint surfaces 41a, 41b, 41c exist between the puffer cylinder 41, moving nozzle 43 and moving main contact 42, and those joint surfaces 41a, 41b, 41c should be located at the upper and lower portions thereof, respectively, based on FIG. 2 to secure machining accuracy on six joint surfaces during the part machining process, thereby making machining difficult and increasing cost.
Furthermore, the first joint surface 41a between the puffer cylinder 41 and moving main contact 42 should preferentially secure assembly dimensions than those of the second joint surface 41b between the puffer cylinder 41 and the coupling portion 43a of the moving nozzle 43, and the third joint surface 41c between the moving main contact 42 and the coupling portion 43a of the moving nozzle 43.
It is because the puffer cylinder 41 and the coupling portion 43a of the moving nozzle 43 are not matched to each other when assembly dimensions are inaccurate on the first joint surface 41a between the puffer cylinder 41 and moving main contact 42, thereby disabling the assembly.
Furthermore, when the assembly dimensions of the first joint surface 41a are not matched to each other, it may cause a problem in securing the conductivity of the circuit breaker as a conductive contactsurface.